A U.S. hydrogen bomb nearly detonated on the nation’s east coast, with a single switch averting a blast which would have been 260 times more powerful than the device that flattened Hiroshima, a newly published book says.

In a recently declassified document, reported in a new book by Eric Schlosser, the supervisor of the nuclear weapons safety department at Sandia national laboratories said that one simple, vulnerable switch prevented nuclear catastrophe.